The present invention relates to a piezoelectric oscillator device and a surface acoustic wave device.
The demand for smaller sizes and lower prices of electronic apparatuses has been becoming stronger recently. Electronic parts used in such electronic apparatuses are required to be smaller-sized and less expensive.
For example, to form an oscillation circuit with a piezoelectric oscillator, such as a quartz oscillator, which provides reference clock frequencies for electronic apparatuses, an amplifier, a condenser and a feedback resistor must be included in addition to the piezoelectric oscillator. These parts are separately formed and connected to each other to form the oscillation circuit.
Recently the amplifier and the feedback resistor for the oscillation circuit has been built in a microcomputer chip, and the piezoelectric oscillator and the condenser, which cannot be accommodated in the chip, are integrated with each other and connected to the chip as a single external part.
A piezoelectric oscillation device including a piezoelectric oscillator and a condenser integrated with each other as shown in FIG. 12 is known (Japanese Patent Laid-Open Publication Tokkaisho 59-178011(1984)).
The piezoelectric oscillation device of FIG. 12 comprises a lower electrode 51 of a paste of Ag, Ag.multidot.Pd or others formed on an alumina substrate 50, a dielectric film 52 of SiO.sub.2 or others formed on the lower electrodes 51, and an upper electrode 53 of a paste of Ag, Age.multidot.Pd or others formed on the dielectric film 52. A piezoelectric oscillator 55 is connected to the upper electrode 53 through a bump 54 of a paste of Ag, Ag.multidot.Pd or others.
To form the lower electrode 51, the dielectric film 52 and the upper electrode 53, the conventional piezoelectric oscillation device of FIG. 12 requires the step of applying and annealing the paste for formation of each layer. In addition, the single layer dielectric film 52 is not sufficient to provide the required characteristics because of a number of voids and holes, and the dielectric film must have at least two layers. Although not shown in FIG. 12, to mount the piezoelectric oscillation device on the surface of a circuit substrate, it is necessary to also form a connection electrode on the underside of the alumina substrate 50.
To form the conventional piezoelectric oscillation device, the application and annealing step is conducted once for the formation of the lower electrode 51, and repeated twice for the formation of the dielectric film 52, once for the formation of the dielectric film 52 and once for the formation of the connection electrode. Thus, this step must be conducted five times. This has added to fabrication costs and has been a barrier to lower product prices.
It is proposed to provide a interdigital electrode on the surface of a dielectric substrate to form a condenser. To obtain the required capacitance, the dielectric substrate must be formed of a dielectric material having a high dielectric constant. Dielectric materials having high dielectric constants do not have sufficient strength, which is necessary technical consideration, for example, adhering the dielectric substrate to a substrate having a sufficient strength. This has added to fabrication costs and has been a barrier to lower part prices.